of a number of small spaces or areolæ, formed by the trabeculæ; in these areolæ is contained the splenic pulp.

The fibroelastic coat, the sheaths of the vessels, and the trabeculæ, are composed of white and yellow elastic fibrous tissues, the latter predominating. It is owing to the presence of the elastic tissue that the spleen possesses a considerable amount of elasticity, which allows of the very great variations in size that it presents under certain circumstances. In addition to these constituents of this tunic, there is found in man a small amount of non-striped muscular fiber; and in some mammalia, e. g., dog, pig, and cat, a large amount, so that the trabeculæ appear to consist chiefly of muscular tissue.

FIG. 1189 Transverse section of the spleen, showing the trabecular tissue and the splenic vein and its tributaries. (See enlarged image)

FIG. 1190 Transverse section of the human spleen, showing the distribution of the splenic artery and its branches. (See enlarged image)

The splenic pulp (pulpa lienis) is a soft mass of a dark reddish-brown color, resembling grumous blood; it consists of a fine reticulum of fibers, continuous with those of the trabeculæ, to which are applied flat, branching cells. The meshes of the reticulum are filled with blood, in which, however, the white corpuscles are found to be in larger proportion than they are in ordinary blood. Large rounded cells, termed splenic cells, are also seen; these are capable of ameboid movement, and often contain pigment and red-blood corpuscles in their interior. The cells of the reticulum each possess a round or oval nucleus, and like the splenic cells, they may contain pigment granules in their cytoplasm; they do not stain deeply with carmine, and in this respect differ from the cells of the Malpighian bodies. In the young spleen, giant cells may also be found,